This project has clearly and extensively defined the host's immune response to chronic stimulation with endogenous viral antigens which are present in spontaneously occurring tumors and are immunologically active as transplantation antigens. The purification and characterization of these antigens are complete resulting in highly specific reagents. These reagents have made possible studies resulting in conceptual advances of our understanding of how the immune responses of the host interact with each other and the transplantation antigens in determining the outcome of the tumor host relationship. The antigens that have been completely studied thus far have been endogenous viral structural proteins. The transforming proteins encoded by the virus, but clearly of host origin, provide potential transplantation antigens that will understandably be of direct importance in human cancer. The project is now focusing on the production of monoclonal antibodies to these proteins that will reuslt in: the evaluation of these proteins as transplantation antigens, a determination of their presence in tumors throughout the phylogenetic scale, and a better understanding of the mechanisms of transformation and thus the means to biochemically or immunologically alter the events that lead to cell transformation.